Hydraulic control system for automatic transmission

ABSTRACT

A hydraulic control system for an automotive automatic transmission using a planetary gear set, the control system having a reverse reaction brake which is applied by the motion of a manual selector valve when the selector valve is set to the neutral position with the engine operating and which is prevented from being applied when the vehicle is being driven in a forward direction and the selector valve is shifted from the drive to the neutral position. The manual selector valve is controlled by a governor pressure which may be connected direct to the source of hydraulic pressure.

United States Patent Irie [ 51 June 6, 1972 [72] Inventor: Namio Irie,Yokohama, Japan [73] Assignee: Nissan Motor Company, Limited,

Kanagawa-ku, Yokohama City, Japan [22] Filed: Apr. 28, 1970 [21 Appl.No.1 32,527

[30] Foreign Application Priority Data Apr. 30, [969 Japan .44/3272O[52] US. Cl. ..74/752 C, 74/864, 74/868, 74/869 [51] Int. Cl. ..Fl6h5/42, B60k 21/00 [58] Field of Search ..74/863, 864, 867-869, 74/752 C[56] References Cited UNITED STATES PATENTS 3,398,607 8/1968 Chana..74/868 X THROTT LINE PRESSURE RE VALVE 3,446,098 5/1969 Searles..74/869 FOREIGN PATENTS OR APPLICATIONS 1,189,637 4/ l 970 GreatBritain ..74/863 Primary ExaminerArthur T. McKeon Attorney.lohn Lezdey Ahydraulic control system for an automotive automatic transmission usinga planetary gear set, the control system having a reverse reaction brakewhich is applied by the motion of a manual selector valve when theselector valve is set to the neutral position with the engine operatingand which is prevented from being applied when the vehicle is beingdriven in a forward direction and the selector valve is shifted from thedrive to the neutral position. The manual selector valve is controlledby a governor pressure which may be connected direct to the source ofhydraulic pressure.

ABSTRACT 3 Claims, 2 Drawing Figures 25 THROTTLE BACK-UP VALVE SOLENOIDDOWN SHIFT VALVE 53 PRESSURE MODIFYING VALVE THROTTLE 5 REDUCER 69 2-3SHIFT I VALVE l-Z SHIFT VALVE MANUAL SELECTOR VALVE PATENTEUJUH 6m 3667,323

SHEET 10F 2 Luv v 4 W MW LU H TIRWIO IRIE. INVENTOR ATT RN PATENTEDJIIII6 I912 LINE E VA LVE PRESSURE R SHEET 2 OF 2 THROTTLE BACK-UP VALVETHROTT VACUMM SENSITIVE SOLENOID 4VALVE oowu SHIFT 2-3 SHIFT TIMINGVALVE 5 VALVE 1:31 ,HPRESSURE MODIFYING VALVE EE'EBIzEk Q VALVE 592-3SH|FT VALVE l-Z SHIFT VALVE MANUAL SELECTOR VALVE exI-uiusTI PORT I'HBNIOIBIE HTIITNYVENTOR ATTOR Y HYDRAULIC CONTROL SYSTEM FOR AUTOMATICTRANSIVIISSION This invention relates to a power transmission of a motorvehicle and, more particularly, to an improved hydraulic control systemof an automotive automatic transmission.

In a usual automotive automatic transmission, an input rotational powerwhich has been carried from a prime mover such as an internal combustionengine to an input shaft is transferred to an output shaft at a selectedrevolution speed and with selected torque through selective actuationand release of friction elements including clutches and brakes whichform part of the transmission. The clutches and brakes, in thisinstance, are intended to act respectively as input clutchestransferring the incoming power and reaction brakes bearing therotational reactive force. When the manual speed selector lever is heldin any of the positions providing forward vehicle speeds, a forwardclutch and forward brake are actuated to provide the selected forwardand, when the selector lever is held in a position providing the reversespeed, then the reverse clutch and reverse brake are actuated to providethe reverse speed. It is thus necessary for effecting the forward orreverse movement of a motor vehicle to have the input clutches andreaction brakes actuated and released selectively. The forward reactionbrake to provide the forward speeds is usually constructed as a one-waybrake which need not be applied when any of the forward speeds is to beselected. When, therefore, the selector lever is shifted to any of thepositions providing any of the forward speeds, the desired forward speedcan be attained readily only by the engagement of the forward clutch,because the one-way brake at all times remains effective on the forwardmovement of the motor vehicle. When, on the contrary, the selector leveris shifted to the reverse position, then the one-way brake remainsinoperable and the reverse can not be attained unless the reverse clutchand reverse brake are actuated concurrently.

Since all the friction elements are kept released when the selectorlever is held in the neutral position in a usual automatic powertransmission, the reverse clutch and reverse brake should be actuatedstimultaneously when the selector lever is shifted from the neutral tothe reverse position. The hydraulic pressure is thus applied to thereverse clutch and reverse brake. This will result in a retardedestablishment of the reverse speed and a production of mechanicalshocks.

It is therefore an object of the invention to provide an improvedhydraulic control system of the nature which is adapted to smoothlyestablish the reverse speed immediately when the selector lever isshifted from the neutral to the reverse position. Such an object can beaccomplished according to the invention without affecting the operationsof the friction elements during high speed driving of the motor vehicle;the reverse brake is kept released even though the selector lever isaccidentally shifted to the neutral position when the vehicle is beingdriven at a high speed.

In the drawings:

FIG. 1 is a schematic view illustrating an example of a power train ofan automatic power transmission of planetary gear type; and

FIG. 2 is a schematic diagram illustrating a fluid circuit of ahydraulic control system implementing the invention.

The power train as shown in FIG. 1 is exemplified as using two planetarygear sets providing three forward and one reverse speeds forillustrative purposes but it will be understood that the hydrauliccontrol system according to the invention may be used with any othertypes of power trains so far as the same is controlled by a hydrauliccontrol system.

Now, the power train shown in FIG. 1 starts with a drive shaft which isconnected to and driven by a prime mover (not shown) such as an internalcombustion engine and terminates with an output shaft 11 which isconnected to and drives a propeller shaft (not shown). The input powerwhich the drive shaft 10 receives from the prime mover is torquemodulated by a torque converter 12 having a propeller or pump 12a,turbine 12b and stator 12c as customary. The

torque converter 12 may be replaced with a fluid coupling, if desired.

The input power in the drive shaft 10 is carried to the propeller orpump 12a and imparts a torque to the turbine 12b which is fast on aninput shaft 13. The stator 12c is secured to a stationary shaft 14through a one-way brake 15, which serves to prevent the stator 12c fromrotating in the direction opposite to the direction of rotation of thedrive shaft 10; this direction of rotation of the drive shaft will behereinafier referred to as the normal direction of rotation.

The power thus imparted to the turbine 12b is then carried to first andsecond planetary gear sets which are generally represented by numerals16 and 17, respectively. The first planetary gear set 16 has rotarymembers including an outer ring gear R, which is internally toothed, twoor more planet pinions P, which are externally meshing with the ringgear R, and a sun gear S, externally meshing with the planet pinions P,.The planet pinion P, is carried by a pinion carrier 18. The secondplanetary gear set 17, similarly, has rotary members including aninternally toothed outer ring gear R two or more planet pinions Pexternally meshing with the ring gear R and carried by a pinion carrier19, and a sun gear 8, externally meshing with the planet pinions P Theserotary members are all rotatable concentrically about a common axiswhich, in the case of the gear train exemplified in FIG. 1, is in linewith a rotary shaft 20 connected to the pinion carrier 18. Asillustrated by way of example, the sun gears S, and S of the first andsecond planetary gear sets 16 and 17, respectively are connected rigidlyto each other through a hollow shaft 21. The pinion carrier 18 isconnected rigidly to the ring gear R of the second planetary gear set 17through the shaft 20 and further to the output shaft 11.

Friction elements are provided which includes a reverse and third-speedclutch 22, a forward clutch 23, a second-speed brake 24, a reverse andfirst-speed brake 25, and a one-way brake 26 which is combined with thereverse and first-speed brake 25.

The reverse and third-speed clutch 22 is operatively connected betweenthe input shaft 13 and the hollow shaft 21 of the sun gears S, and 5,through a brake drum 27 and the forward clutch 23 is operativelyconnected between the input shaft 13 and the ring gear R, of the firstplanetary gear set 17 through an intermediate shaft 28, as shown. Thesecond-speed brake 24 is operatively connected between the clutch 22 andthe hollow shaft 21 and forced against the brake drum 27 to hold the sungears S, and S stationary when applied. The reverse and first speedbrake 25, on the other hand, is operatively connected to the pinioncarrier 19 of the second planetary gear set 17 and, when applied, holdsthe planet pinions P stationary. The one-way brake 26 acts to preventthe pinion carrier 19 from rotating in the direction opposite to thenormal direction of rotation of the drive shaft 10.

When, now, the manual speed selector (not shown) is shifted from theneutral to the first-speed position, then the clutch 23 is coupled sothat the ring gear R, of the first planetary gear set 16 is driven. Apower providing the first forward speed is delivered from the pinioncarrier 18 of the first planetary gear set 16 to the output shaft 11. Inthis instance, the pinion carrier 19 tends to rotate in the directionopposite to the normal direction previously defined because of therunning resistance carried thereto from the wheel axles (not shown).Such tendency of the pinion carrier 19 is, however, blocked by theaction of the one-way brake 26 and thus streamlined shifting to thefirst speed can be effected. When, however, the selector lever isshifted from the neutral to the reverse position, then the clutch 22 iscoupled and the brake 25 applied. The sun gears S, and S, are thusdriven by the input shaft 13. If, in this instance, the brake 25 is notapplied, then the pinion carrier 19 will tend to rotate in the normaldirection and, as a consequence, the second planetary gear set will tendto rotate in its entirety in the normal direction, obstructing theoutput shaft 11 from rotating in the opposite direction. This is thereason why two friction elements should The drawback of this nature asexperienced where the power train as shown is used in combination withan existing hydraulic control system will be eliminated if the samepower train is used together with the hydraulic control systems illus-The hydraulic control system as illustrated in FIG.

pressure adjustment the hydraulic conduit is connected to a manual speedselector valve 38 provided with a slidable spool 39, to a solenoiddown-shift valve 40 provided with a slidable spool 41 and to a vacuumthrottle valve 42 provided with a slidable spool 43. V H

First and second governor valves 44 and 44, respectively, which areconnected by a conduit 45, supply pressurized oil through a conduit 46to a first-to-second speed shift valve 47, which will be hereinafterreferred to as a 1-2 shift valve and which is provided with a slidablespool 48 and a spring 49, to a second-to-third speed shift valve 50which is hereinafter referred to as a 2-3 shift valve and which isprovided with a slidable spool 51 and a spring 52, to a cut-back valve53 provided with a slidable spool 54 and a spring 55, and to a by-passvalve 56 provided with a slidable spool 57 and a spring 58. The springs49, 52, 55 and 58 are selected in an increasing governor pressureresisting order and therefore a predetermined relatively low governorpressure in the conduit 46 applied against an end land 59 of the spool48 of the I-2 shift valve 47 overpowers the force of the spring 49 tomove the spool 48 leftwardly in the drawing. It should be noted that allthe valve spools are shown in both inactivated and activated positions,the lower halves of'the spools 48, 51 and 54 in the former and the upperhalves in the latter position.

The vacuum throttle valve 42 is connected through a diaphragm assembly60 to the engine intake manifold (not shown) and throttles the pressurein the main conduit 33 to a throttle pressure which is fed throughconduit 61 to the throttling end 62 of the 2-3 shift valve 50, to theupper end of the spool' 57 of the by-pass valve 56 acting together withthe spring 58 against the governor pressure applied on the spool 57 fromthe conduit 46 connected to the lower end of the valve 56, to the endland of the spool 36 of the pressure regulator valve 34 and through thecut-back valve 53 via a conduit 63 to the end land 64 of the spool 35 ofthe pressure regulator valve 34. The vacuum throttle valve 42 is furtherconnected to a throttle back-up valve 65, which is provided with a spool66, through a conduit 67 receiving the surplus oil resulting fromthrottling of the valve vacuum throttle valve 42. The throttle back-upvalve 65 is connected through a conduit 68 to the manual selector valve38, through a conduit 69 to the reverse and first-speed brake 25 and tothe 1-2 shift valve 47, and through the conduit 68 to the solenoiddown-shift valve 40. The down-shift valve 40 is connected through aconduit 70 to the 2-3 shift valve 50 and the l-2 shift valve 47 A Themanual selector valve 38 is further connected through a conduit 71 and aconduit 72 to a second-speed lock valve 73 which is provided with aspool 74 and a spring 75, to the 2-3 shift valve 50, and the regulatorvalve 34 through a conduit 76, and to the l-2 shift valve 47 through aconduit 77 and a conduit'78, which is also connecting to the forwardclutch motor (not shown). A check valve 79 is provided which has anorifice (not identified by a numeral) in the valve head to slow down theflow of pressurized oil in the conduit 71 connecting with the 2-3 shiftvalve 50. A conduit 80 connects the two shift valves 47 and 50,supplying throttle pressure from the conduit 61 through the throttlingend 62 of the 2-3 shifi valve 50 to the l-2 shift valve 47. The lockvalve 73 connects through a conduit 81 the 1-2 shift valve 47 to theapply side 82 of a servo motor 83 of the brake band 24. The2-3 shiftvalve 50 is connected through a conduit 84 to the release side 85 of theservo motor 83. The conduit 84 branches off into a conduit 86, providedwith an orifice 87 and the by-pass valve 56, leading to a clutch motor(not shown) of the reverse and third-speed clutch. It should be noted,that as in the case of the spools 48, 51 and 53, the spools 35, 36, 41,43, 57 and 74 of the respective valves 34, 40, 42, 56 and 73 are shownin both inactivated and activated positions, the right hand halves inthe former and the left hand halves in the latter positions, however,the valve 65 spool 66 halves are shown in reversed positions.

The torque converter 12 receives pressurized fluid from the regulatorvalve 34 through a conduit 88. This circuit is provided with necessaryrelief valves as shown in the left-hand bottom portion of the drawingalthough no numerals are used for their identification.

The manual selector valve 38 has ports a, b, c, d, e, f and g which canbe connected with the main hydraulic conduit 33 by moving the spool 39into various positions with a selector lever (not shown). According tothis invention, the selector valve 38 and the spool 39 are soconstructed that the main hydraulic conduit 33 communicates with theports d, e and f when the selector lever (not shown) is in the neutralposition. The port e is connected to the 1-2 shift valve 47 by theconduit 77. The l-2 shift valve 47 serves as the control valve in thisinvention, connecting, when inactivated, the conduit 77 to the conduit69, which therefore becomes pressurized and causes the reverse reactionbrake 25 to engage. Furthermore, should the selector lever (not shown)be shifted from the first to the neutral position accidentally whiledriving at a high speed (at the second or third speed), the 1-2 shiftvalve 47 serves even in this case as the control valve by remaining inthe actuated position, thus preventing the conduit 77 from communicatingwith the conduit 69. The reverse reaction brake 25 remains disengaged inthis manner, as will be described hereinafter in more detail.

It is believed that only a brief description of the operation of thehydraulic circuit suffices, since the improvement of the invention canbe applied to any kind of control system of an automatic transmissionproviding forward and reverse speeds. Therefore, reference is made nowto Table I in which the various ports of the selector valve 38 are shownopen correspond ing to the positions P (parking), R (reverse), N(neutral), D (drive range), ll (manual second speed range), and I(manual first speed range), and in which also the friction elements thatwhich are engaged corresponding to the above mentioned positions areindicated by a symbol and those friction elements remaining inoperativeby a symbol TABLE I Actuated friction elements Clutch Brake Operativeports of Mode ofoperatlons selectorvalva 38 22 23 24 26 26 e o e dDrlgetrange:

s 2d a b c i 3d Ifthe manual selector valve 38 is set to the drive rangeposition (D), the spool 39 of the valve 38 is moved so that the linepressure conduit 33 is brought into communication with the ports a, band c as seen in FIG. 2. The port a is connected to the lock valve 73and the 2-3 shift valve 50 by the conduit 71. The port b is connected tothe lock valve 73 by the conduit 72.

The port 0 is connected to the 1-2 shift valve 47 and a motor (notshown) of the forward clutch 23 by the conduit 78 (FIG 2) to engage theforward clutch 23, which serves as a forward input clutch (Table l). Thepower from the engine to the torque converter 12 passes through theinput shaft 13 to the forward clutch 23 and is transmitted through theintermediate shaft 28 to the ring gear R of the first planetary gear set16. The ring gear R, causes the pinions P, to rotate in the normaldirection. Therefore, the sun gear S, rotates in the reverse directioncausing the sun gear S of the second planetary gear set 17 to rotate inthe reverse direction, whereby the pinions P of the second planetarygear set 17 rotate in the normal direction. The one-way brake 26 nowprevents the sun gear S from reversing the rotation of the pinioncarrier 19 and acts as a forward reaction brake. The ring gear R of thesecond planetary gear set 17 rotates in the nonnal direction. Thus, theoutput shaft 11 rotating with the ring gear R also rotates in the normaldirection (FIG. 1), thereby providing a reduction ratio corresponding toa first forward speed.

As the speed of the vehicle is increased in this state, the oil pressurein the governor pressure conduit 46 applied on the end land 59 of thespool 48 also increases and overcomes the biassing force of the spring49 of the 1-2 shift valve 47, thereby forcing the spool 48 of the 1-2shift valve 47 to move leftwardly, whereby the main hydraulic conduit 33communicates through the conduit 78 with the conduit 81 and with thelock valve 73. For the first forward speed, the line pressures areintroduced from the conduits 71 and 72 into the lock valve 73 and thearea to which the pressure from the conduit 71 is exerted is greaterthan the area to which the pressure from the conduit 72 is exerted, and,for this reason, the spool 74 of the lock valve 73 is urged upward toconnect the now pressurized conduit 81 with the apply side 82 of theservo motor 83, thereby engaging the second-speed brake 24 (FIG. 2). Theone-way brake 26 is simultaneously disengaged. As is the case with thefirst forward speed, the power from the input shaft 13 is transmittedthrough the forward clutch 23 to the ring gear R,. The brake 24 holdsthe drum 27 stationary to prevent the rotation of the sun gears S, and Sand thus serves as a forward reaction brake. The pinions P, rotate andrevolve about the sun gear S, which is now held stationary, so that thepinion carrier 18 and the output shaft 11 integral therewith rotate inthe normal direction at a speed higher than the first forward speed(FIG. 1), thereby providing a reduction ratio corresponding to thesecond forward speed.

As the speed of the vehicle is further increased so that the oilpressure in the governor pressure conduit 46, applied on the end land ofthe spool 51, overcomes the combined forces of the spring 52 of the 2-3shift valve 50 and the oil pressure from the throttle pressure conduit61 to force the spool 51 of the 2-3 shift valve 50 to move leftwardly inthe drawing, the oil pressure passing through the conduit 71 and thecheck valve 79 with an orifice (not identified by a numeral) into theconduit 84' and the release side 85 of the servo motor 83 to release thebrake 24, and further communicates through the conduit 86 and orifice 87with the motor (not shown) of the clutch 22 which is consequentlycoupled (FIG. 2) The power transmitted to the input shaft 13 is furthertransmitted to the ring gear R, through the forward clutch 23, and tothe sun gear S, through the clutch 22. As a result, the ring gear R, andsun gear S, are interlocked with each other and rotate in the normaldirection with the pinion carrier 18 and output shaft 11 rotating at thesame speed as the input speed 13 (FIG. 1), thereby providing a thirdforward speed. In this instance, the clutches 22 and 23 serve as inputclutches and no reaction is produced because the torque is notincreased.

If the speed selector lever (not shown) is set to the manual secondforward speed position (11) the spool 39 of the selector valve 38 ismoved to cause the main hydraulic conduit 33 to communicate with theports b, c and d (Table I). The port b communicates with the lock valve73 through the conduit 72. Since the conduit 71 is drained, the spool 74of the lock valve 73 is forced downward by the pressure in the conduit72 which thereby communicates with the conduit 81 to engage the brake24. The port 0 communicates with the 1-2 shift valve 47 and the motor(not shown) of the forward clutch 23 through the conduit 78, therebyengaging the forward clutch 23. The port d communicates with thesolenoid down-shift valve 40 and throttle back-up valve 65 through theconduit 68. Since the circuit 71 is drained, the brake 24 remainsapplied even if the speed of the vehicle is increased, and the clutch 22remains disengaged, whereby the manual second forward speed ismaintained (FIGS. 1 and 2).

When the speed selector lever (not shown) is set to the manual firstforward speed position (I), the spool 39 of the selector valve 38 ismoved to cause the main hydraulic conduit 38 to communicate with theports 0, d and e (Table l). The port 0 communicates with the I-2 shiftvalve 47 and the motor (not shown) of the forward clutch through theconduit 78 to engage the forward clutch 23. The conditions ofcommunication of the port d are the same as in the case of the manualsecond forward speed position (II), and the port 2 communicates with theI2 shift valve 47 through the conduit 77 and, when the spool 48 of the1-2 shift valve 47 is forced rightward by the spring 49, the inlet ecommunicates with the motor (not shown) of the brake 25 through theconduit 69 to engage the brake 25 (FIG. 2). Since the conduit 72 isdrained, the brake 24 remains disengaged and the oil pressure in theconduit 69, together with the force of the spring 49 of the l- 2 shiftvalve 47, forces the spool 48 of the l-2 shift valve 42 to hold itsrightward position (the governor pressure being low at low driven shaftspeeds), whereby the manual first forward speed is maintained. Since thepinions P of the second planetary gear set 17 are now driven by theoutput shaft 11 because the reverse brake 25 is engaged, the sun gear Sis also driven to cause braking on the engine (FIG. 1

If the speed selector lever (not shown) is set to the reverse position(R), the spool 39 of the selector valve 38 is moved to cause the mainhydraulic conduit 33 to communicate with the ports a, e and g. Theconditions of communication of the ports d and e are the same as thosein the case of the manual first forward speed position and the reversedbrake 25 is engaged this time. The port g communicates with the port fvia a conduit 89 and with the motor (not shown) of the clutch 22 throughthe conduit 76, 2-3 shift valve 50 and conduits 84 and 86 by-passing theorifice 87 through the by-pass valve 56 to engage the reverse clutch 22.Simultaneously the pressure in the conduit 76 acts on the regulatorvalve spool 36, increasing the pressure in the hydraulic conduit 33. Thepower transmitted to the input shaft 13 is thus transmitted by theclutch 22 through the drum 27 to the sun gear S Since the pinion carrier19 is held stationary by the action of the brake 25, the pinions P nowidle away, causing the ring gear R and output shaft 11 to rotate in thereverse direction. In this instance, the reverse clutch 22 serves as areverse input clutch and the reverse brake 25 serves as a reversereaction brake.

When the manual selector valve 38 is shifted to the parking position(P), the spool 39 thereof is moved to cause the ports e and dcommunicate with the main hydraulic conduit 33, thereby engaging thereverse brake 25 as is the case with the neutral position (N).

In the conventional automatic transmission control systems, the manualselector valve and the valve spool are constructed to close the inlet ofthe main hydraulic conduit thereby to disengage all the clutches andbrakes when the selector valve ,is in the neutral position. When theselector valve is shifted from the neutral to the reverse position forbacking-up, a pressurized fluid must be supplied to the reverse inputclutch motor and the reverse reaction brake motor to engage the twofriction elements simultaneously, requiring a considerable length oftime. Furthermore, the timing for depressing the accelerator pedal is sodifficult and often premature that as soon as the engagement of thefriction elements is complete, the coupling (which is the torqueconverter in this embodiment), which has been rotating without anyresistance, will suddenly receive such a resistance as to cause a shockor jerk to the vehicle. Also, the reduction ratio is greater in thepower train for backingup than in the manual first forward speed, wheretwo friction elements are engaged at the same time. Because of thehigher reduction ratio, a higher torque is required and accordingly, ahigher hydraulic pressure must be used to effectively engage thefriction elements, the pressure builds-up to further prolong the timerequired for completion of the engagement.

According to the present invention, the manual selector valve isconstructed to engage the reverse reaction brake even when thetransmission is in the neutral position, as mentioned above. Apressurized fluid passes from the main hydraulic conduit 33 to the porte, conduit 77 and through the l 2 shift valve 47 and the conduit 69 tothe motor (not shown) of the reverse brake 25 motor so as to engage'thebrake 25, as mentioned above. As a result, the transmission is quicklyset into a reversing condition, when the selector valve 38 is shiftedfrom the neutral to the reverse position and the necessity of timing thedepression of the accelerator pedal is eliminated, whereby the movementfrom a halt into a reverse direction is facilitated and is smoothly andquickly accomplished.

When the manual selector valve is in the neutral position, the reverseinput clutch is not engaged and therefore the planetary gear set typetransmission is not rotated and the vehicle remains stationary.

- However, should the manual selector valve be shifted accidentallyduring high speed driving from the drive to the neutral position, allthe friction elements would be disengaged except the brake 25. Thetransmission would run by the driving wheels of the vehicle through theoutput shaft 11, ring gear R,, pinions l9 and sun gear S, at a speedhigher than the output shaft ll speed because the reverse brake 25prevents the rotation of the pinion carrier 19, thus possibly causing adamage to the transmission mechanism.

e To avoid such a possible damage, according to this invention, thefirst governor valve 44 is connected directly to the I main hydraulicconduit 33 through a conduit 33a as shown by a dotted line in FIG. 2,instead of the connection through the selector valve 38 as shown in FIG.2. Therefore, during high speed driving, the governor pressure appliedthrough conduit 33 on the end land 59 of the 1-2 shift valve spool 48maintains its'activated, position in which the conduit 77 is prohibitedfrom communicating with the conduit 69 and the brake 25 thus remainsdisengaged.

According to prior art, the governor valve 44 is connected to the mainhydraulic conduit 33 only when the selector valve 38 is in the drive,second manual forward speed or first manual forward speed position.However, according to this invention, the governor valve 44 is suppliedwith a pressurized fluid at all times so far as the oilpump 32 isrunning, regardless of the position of the manual selector valve 38.

A feature of this invention is, that the l-2 shift valve 47 has a dualfunction. In addition to effecting the shifting from the first to thesecond speed ratio at a predetermined governor pressure, it functions asthe control valve by passing a pressurized fluid from the manualselector valve 38 to the motor (not shown) of the reverse brake 25 whenthe selector valve is in the neutral position but does not pass thepressurized fluid to the motor of the brake 25 if the selector valvehappens to be shifted from the drive to the neutral position while thevehicle is driven at a high speed.

The control system described above is understood to be an illustrativesystem only and that the invention is not to be limited to the specificconstructions, arrangements and devices shown.

What is claimed is:

1. In an automatic transmission for a motor vehicle having a low reversereaction brake for placing the planetary gear sets in reverse drive, ahydraulic control system comprising a source of hydraulic pressure; anda manual selector valve communicating with said source of hydraulicpressure and having a conduit communicating with said low reverse brakewhen said automatic transmission is set in its neutral position, wherebywhen the manual selector valve is shifted from neutral to reverseposition the reverse high clutch transmits power from the driving memberto the sun gear of a planetary gear set and the low reverse reactionbrake acts to hold the planet carrier of said gear set stationary so asto cause the ring gear of said gear set and the driven member to rotatein reverse.

2. A hydraulic control system according to claim 1 including governorvalve means forming asource of governor pressure and a l-2 shift valvecommunicating with said source of governor pressure and with said manualselector valve, said l-2 shift valve having a valve spool and a speedresponsive means for holding said valve spool in a first position whensaid speed responsive pressure is below a predetermined level and in asecond position when said speed responsive pressure exceeds saidpredetermined level, said valve spool blocking fluid communicationbetween said low reverse reaction brake and said manual selector valvewhen said l-2 shift valve is in said second position, whereby said 1-2shift valve passing pressurized fluid from said manual selector valve tosaid low reverse reaction brake when said selector valve is in theneutral position and does not pass pressurized fluid to said low reversereaction brake when said manual selector valve is from the drive to theneutral position when said vehicle is at high speed.

3. In an automatic transmission for a motor vehicle having a drivingmember; a driven member; a first and second planetary gear set eachhaving toothed members comprising an outer ring gear, at least twoplanet pinions carried by a carrier and meshing with said outer gear anda sun gear externally meshing with said planet pinions; a shaftconnecting said sun gears of said first and second gear sets to eachother; shaft means connecting said first and second planetary gear setwith said driving member and said driven member, and clutch and brakemeans for controlling the relative motion of said planetary gear sets,the clutch and brake means including a reverse high clutch and a lowreverse reaction brake means for operatively connecting said reversehigh clutch and reverse reaction brake to said driving member and theshaft connecting said sun gears for placing the planetary gear sets inreverse drive, a hydraulic control system comprising a source ofhydraulic pressure, and a manual selector valve communicating with a thesecond gear set is held stationary by said brake, the pinions of saidsecond gear set idle away causing the outer ring gear of said secondgear set and the driven member to reverse direction.

*wr-rse

1. In an automatic transmission for a motor vehicle having a drivingmember, a driven member, a plurality of planetary gear sets drivablyconnected with said driving and driven members by means of a shaft andclutch and brake means for controlling the relative motion of theplanetary gear sets, the clutch and brake means including a reverse highclutch and a low reverse reaction brake for placing the planetary gearsets in reverse drive, a hydraulic control system comprising a source ofhydraulic pressure; and a manual selector valve communicating with saidsource of hydraulic pressure and having a conduit communicating withsaid low reverse brake when said automatic transmission is set in itsneutral position, whereby when the manual selector valve is shifted fromneutral to reverse position the reverse high clutch transmits power fromthe driving member to the sun gear of a planetary gear set and the lowreverse reaction brake acts to hold the planet carrier of said gear setstationary so as to cause the ring gear of said gear set and the drivenmember to rotate in reverse.
 2. A hydraulic control system according toclaim 1 including governor valve means forming a source of governorpressure and a 1-2 shift valve communicating with said sourcE ofgovernor pressure and with said manual selector valve, said 1-2 shiftvalve having a valve spool and a speed responsive means for holding saidvalve spool in a first position when said speed responsive pressure isbelow a predetermined level and in a second position when said speedresponsive pressure exceeds said predetermined level, said valve spoolblocking fluid communication between said low reverse reaction brake andsaid manual selector valve when said 1-2 shift valve is in said secondposition, whereby said 1-2 shift valve passing pressurized fluid fromsaid manual selector valve to said low reverse reaction brake when saidselector valve is in the neutral position and does not pass pressurizedfluid to said low reverse reaction brake when said manual selector valveis from the drive to the neutral position when said vehicle is at highspeed.
 3. In an automatic transmission for a motor vehicle having adriving member; a driven member; a first and second planetary gear seteach having toothed members comprising an outer ring gear, at least twoplanet pinions carried by a carrier and meshing with said outer gear anda sun gear externally meshing with said planet pinions; a shaftconnecting said sun gears of said first and second gear sets to eachother; shaft means connecting said first and second planetary gear setwith said driving member and said driven member, and clutch and brakemeans for controlling the relative motion of said planetary gear sets,the clutch and brake means including a reverse high clutch and a lowreverse reaction brake means for operatively connecting said reversehigh clutch and reverse reaction brake to said driving member and theshaft connecting said sun gears for placing the planetary gear sets inreverse drive, a hydraulic control system comprising a source ofhydraulic pressure, and a manual selector valve communicating with asource of hydraulic pressure and having a conduit communicating withsaid low reverse brake when said automatic transmission is set in itsneutral position, whereby when the manual selector valve is shifted fromneutral to reverse position the reverse high clutch is coupled andtransmits power to the sun gear of said second gear set through thebrake drum and the reverse reaction brake is applied, the pinion carrierof the second gear set is held stationary by said brake, the pinions ofsaid second gear set idle away causing the outer ring gear of saidsecond gear set and the driven member to reverse direction.